The present invention relates to a method of preparing polycarbonate.
Polycarbonates are generally produced through one of two types of processes: an interfacial process or a melt transesterification process. In the melt transesterification process, dihydroxy compounds such as biphenol A are reacted with a carbonic acid diester. For many purposes, the carbonic acid diester may be a diaryl carbonate such as diphenyl carbonate.
It is also known to use the melt transesterification process with activated diaryl carbonates. For example, U.S. Pat. No. 4,323,668 describes a polycarbonate transesterification process comprising reacting (ortho-alkoxycarbonylaryl)carbonates and a dihydric phenol under transesterification reaction conditions. In the specific examples, U.S. Pat. No. 4,323,668 makes uses of bis-methylsalicylcarbonate (BMSC) as the diaryl carbonate. Use of activated diaryl carbonates is also described in U.S. Pat. Nos. 6,420,512, 6,506,871, 6,548,623, 6,790,929, 6,518,391, US 2003/0139529, and US 2003/0149223. When these activated carbonates are used, internal residues and end-caps derived from the activated diaryl carbonate are incorporated into the final polymer. See, US patent Publication No. 20030050427 and 20030149223.